Exemplary embodiments of the invention relate to a separating device for a fluid from a fuel cell system, wherein the fluid has a water and a gas portion, with a fluid inlet for supplying the fluid, with a fluid outlet for removing the fluid or a portion thereof, with an outlet valve which controls the fluid outlet and with a first reservoir region, in which the water portion of the fluid is collected, wherein the first reservoir region comprises a first outlet in order to feed the water portion in the direction of the fluid outlet. Exemplary embodiments of the invention also relate to a fuel cell system with the separating device and to a method for operating the separating device.
Fuel cell systems convert chemical energy into electrical energy. For this purpose a fuel, mostly hydrogen, is mixed by means of an electrochemical process with an oxidant, mostly ambient air, in order to generate the electrical energy. The electrochemical process produces very clean outlet gases, as well as water that can advantageously be used in part to moisten a membrane of the fuel cells or the oxidant in the fuel cell system. However, the production of the water portion is so great that during a fairly long operation water must be removed from the fuel cell system. The removal of the water portion can be realized, for example, by a removal line which is connected by means of a valve.
In particular in the case of fuel cell systems in which the partially consumed fuel is recirculated from a fuel cell outlet in a circulation branch into a fuel cell inlet the gas present in the recirculation branch or in the fuel cell can become contaminated, for example, by nitrogen (N2). In this case in many fuel cell systems a drain line—a so-called purge line—is provided, via which the gas can be separated from the recirculation branch or from the fuel cell in an impulse-like manner.
Since the fuel cell systems are intended to be used and are used as an energy source suitable for everyday use for driving vehicles, the fuel cell systems must also be able to work in a reliable way with changing environmental conditions. In particular, freezing of the water portion in the fuel cell system constitutes a technical challenge. For this reason it is possible to provide the drain lines for the water and the gas separately with two outlet valves so that when the water portion freezes the gas can still be reliably expelled via the second drain line.
German patent document DE 11 2007 002 278 T5 discloses using a gas/water discharge valve in a fuel cell system for simultaneous realization of the discharge of gas and water. The number of outlet valves can thus be reduced. The problem of freezing of the water portion is averted in that the water temperature is detected by means of a sensor and an expulsion of the gas/water portion only takes place when the water temperature exceeds a predefined threshold.
Exemplary embodiments of the present invention are directed to a separating device for a fuel cell system having a reliable operating behavior. Exemplary embodiments of the present invention are also directed to a fuel cell system with the separating device and a method for operating the separating device.
Within the scope of the invention a separating device is provided that is suitable and/or designed for a fluid from a fuel cell system. The fluid comprises a water and a gas portion. The gas portion is particularly preferably formed by fuel, in particular hydrogen, from the fuel cell system possibly with impurities such as, for example, nitrogen. The water portion is in gaseous or liquid form and has preferably been formed by the electrochemical conversion of the fuel and the oxidant in the fuel cell system.
The separating device comprises a fluid inlet, via which the fluid is fed, for example, from a fuel cell stack of the fuel cell system. The separating device further comprises a fluid outlet, via which the fluid or parts thereof are removed. The fluid outlet can be controlled through an outlet valve. In particular the fluid outlet can be opened and closed by the outlet valve.
The separating device is formed to separate the water portion from the fluid and to expel the water portion and/or the gas portion via the fluid outlet, e.g. into the environment or in the direction of a consumer.
Particularly preferably the separating device comprises precisely one fluid outlet for removing or expelling and/or precisely one outlet valve, wherein both the water portion and the gas portion can be removed or expelled via this common fluid outlet or via the common outlet valve.
In the separating device a first reservoir region is provided, in which the water portion, in particular the liquid water portion, of the fluid is collected and which comprises a first outlet in order to convey the water portion in the direction of the fluid outlet. In the first reservoir region the water portion is thus brought together wherein the first reservoir region is connected in terms of flow to the fluid outlet, wherein—as set out further below—further flow elements and components can be intermediately arranged.
Within the scope of the invention the separating device should include a second reservoir region comprising a second outlet, which feeds or further feeds the water portion in the direction of the fluid outlet. The first reservoir region is thus initially connected in series in terms of flow via the first outlet to the second reservoir region and the second reservoir region via the second outlet to the fluid outlet.
A water portion can thus flow from the first reservoir region via the first outlet into the second reservoir region and then via the second outlet into the fluid outlet. In particular, this flow path is the only connection between the first reservoir region and the fluid outlet for the liquid water portion in regular operation, i.e. without overflowing of the first reservoir region.
If one considers a proper installation position of the separating device the first outlet is arranged lower than the second outlet. The height difference between the first and the second outlet leads to deposits of the water portion being hindered from flowing away in the first and the second reservoir region below the second outlet whereby these deposits completely cover the first outlet. It is thus constructively predefined that the first outlet that connects the first reservoir region and the second reservoir region is always completely covered by the deposits of the water portion.
It is thereby a consideration of the invention that it is advantageous to provide the outflow of the water portion and the gas portion via a common fluid outlet and preferably via a common outlet valve. To date there was the problem that this common fluid outlet can freeze at temperatures below 0° C. due to the water portion and thus block both the removal of the water portion and also the gas portion.
Due to the fact that the separating device is designed so that deposits of the water portion constantly remain in the separating device that completely cover the first outlet the problem of freezing of the common fluid outlet or the common outlet valve is elegantly solved: At temperatures below 0° C. these deposits of the water portion will naturally freeze. The first outlet is thereby closed in a reliable manner for the process. Flowing away of the water portion from the first reservoir region into the fluid outlet is prevented so long as the deposits of the water portion have frozen and the first outlet is thereby completely closed.
The gas portion can, on the other hand, pass freely through the fluid outlet so that also in operation below 0° C. and with frozen deposits of the water portion the gas portion can be reliably expelled via the fluid outlet and the outlet valve.
The separating device preferably comprises a gas feed device for feeding the gas portion that is coupled in terms of flow with the fluid outlet and which comprises an inlet above the first and/or second outlet. The inlet is preferably arranged so that even with a greatly filled reservoir region, thus with a higher fluid level, the gas portion can be fed without hindrance to the fluid outlet.
With a possible constructive embodiment of the invention the first outlet is incorporated in or on a first pipe body and the second outlet in or on a second pipe body, wherein the second pipe body is arranged within the first pipe body. The inner space of the second pipe body is connected in terms of flow with the fluid outlet and additionally forms the gas feed device. The water portion is thus fed through the first outlet into an intermediate space between the pipe bodies and then via the second outlet to the fluid outlet. The gas portion can on the other hand pass through an open end section or further passages as an inlet in the second pipe body and independently of the water portion reach the fluid outlet.
In principle it is also possible that the cross-section of the first and the second pipe body is designed, for example, in the manner of a polygon or with multiple corners or has a free form. It is also possible for the pipe bodies to respectively be formed as multi-part components.
In a particularly preferred embodiment of the invention, which can be implemented particularly simply in terms of production, the first and/or the second pipe body are formed as a straight hollow cylinder, thus as a pipe with circular cross-section, and are arranged coaxially and/or concentrically in relation to each other. The first reservoir region is thus, radially observed, outside of the first pipe body and the second reservoir region between the two pipe bodies. The first outlet can be formed as one or more passage openings or perforations in the bottom region of the first pipe body, the second outlet in the same variations but offset in height in relation to the first outlet.
In a possible embodiment of the invention it is claimed that the upper edge or at least a section of the upper edge of the first pipe body is arranged lower than the upper edge or at least a part section of the upper edge of the second pipe body. This embodiment is based upon the consideration that when the first outlet is closed and during operation of the fuel cell system the level increases in the first reservoir region. In order to now ensure that the gas portion can reliably reach the fluid outlet at any time the upper edges are selected so that the water portion initially reaches the upper edge of the first pipe body and then enters the second reservoir region. It can be provided that the water portion can flow away via the second outlet into the fluid outlet or—on the basis of the still present frozen deposits—also freezes and likewise closes the second outlet. In the last case the water portion can further increase until the upper edge of the second pipe body is reached. It is only at this level that the water portion can again reach the fluid outlet. An additional safety reserve in frost operation is thus produced through the offset of the upper edges of the two pipe bodies.
In an alternative of the invention the height of the upper edge or at least a section of the upper edge of the first pipe body is arranged higher than the upper edge or at least a partial section of the upper edge of the second pipe body. This embodiment ensures that if the first outlet is frozen the level must rise very high until the water portion can reach the fluid outlet or the second outlet.
In a possible further development of the invention the first reservoir region comprises a bottom section and a supply section wherein the bottom section assumes in a horizontal plane, in particular in the middle, a smaller area than the supply section. The bottom section is preferably dimensioned in height so that it ends at the same height with the second outlet so that the deposits are fixed through the bottom section. This further development of the invention is based upon the consideration that the whole heat capacity of the deposits of the water portion is kept low in the bottom section in that the volume available is kept low in the bottom section for the water portion.
In case of a start-up of the fuel cell system with a frozen start therefore only the comparatively narrow bottom section must thaw until it is possible to dispose of the water portion again via the fluid outlet.
A further aspect of the invention relates to a fuel cell system for a vehicle with one or more fuel cell stacks and also a separating device as was previously described.
In a first alternative the separating device can be arranged in a recirculation branch that recirculates partially consumed fuel gas from the fuel cell stack into the fuel cell stack.
In a second alternative embodiment the separating device is arranged in an outlet branch that discharges partially consumed fuel gas from the fuel cell stack.
In a third alternative embodiment the separating device is arranged in an outlet branch that discharges moistened oxidant gas from a water-heat exchanger.
In the first two embodiments mentioned the gas portion is formed as a mixture of fuel, in particular hydrogen, and impurities such as for example nitrogen. In the third alternative the gas is formed as an ambient air.
In order to bring the separating device as quickly as possible into an operation-ready state to output the water portion the separating device can be thermally coupled with the fuel cell stack in order to accelerate the thawing of the deposits.
It is particularly preferably provided that the thermal coupling is designed so that the heat flow preferably initially reaches the supply section and subsequently the bottom section in order to ensure that the deposits are only thawed in the bottom section when the water portion has reached a temperature in a supply section that allows safe drainage through the fluid outlet or through the outlet valve.
The separating device is particularly preferably tempered through a coolant from the cooling circuit of the fuel cell stack. The coolant is brought very early through the fuel cell stack to a temperature above 0° C. so that a quick heating of the separating device takes place through the tempering of the separating device by means of the coolant. The coolant can also flow through the separating device, the heat flow thus takes place via convection.
In alternative embodiments the separating device is flanged, for example, with a flange planarly against a warm region of the fuel cell stack so that the heat flow is realized through heat conduction.
A further aspect of the invention relates to a method for operating the previously described separating device and/or the fuel cell system with the separating device as previously described. In particular the subject matter relates to a method for securing the separating device.
In the method during the operation of the separating device a water portion of the fluid is collected in the first and in the second reservoir region. Already during the collection of the fluid the water portion runs out via the first and the second outlet. Due to the height difference of the outlets, however, deposits of the water portion are prevented from flowing away, wherein the deposits completely cover the first outlet. In case of freezing of the deposits the first outlet is blocked so that no water portion can pass via the first outlet into the fluid outlet.
When the separating device is thawed the deposits are thawed through heating of the fuel cell system, wherein after thawing the first outlet can be passed through in terms of flow so that after thawing a water portion can pass via the first outlet into the fluid outlet.